Apparatus and method for image projection using dichroic mirror wheel

ABSTRACT

An image projecting apparatus including a light source emits a plurality of monochromatic rays of light with different wavelengths. A condenser lens concentrates the plurality of monochromatic rays. A first color separating unit rotates and selectively causes the plurality of monochromatic rays to be reflected therefrom or passed therethrough. A second color separating unit selectively causes the plurality of monochromatic rays that are passed through the first color separating unit to be reflected therefrom or passed therethrough. A square beam generating unit is inputted with the plurality of monochromatic rays reflected from the first and the second color separating units and transforms the monochromatic rays as inputted into square beams. A panel unit is inputted with the square beams of the monochromatic rays and forms a plurality of monochromatic images corresponding to the monochromatic rays.

[0001] This application claims the priority of Korean Patent ApplicationNo. 2002-28024, filed May 21, 2002 in the Korean Intellectual PropertyOffice, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention generally relates to an image projectingapparatus using a dichroic mirror wheel, and more particularly, itrelates to an image projecting apparatus capable of minimizing a lightloss and improving brightness by using a pair of dichroic mirror wheels,and a method therefor.

[0004] 2. Description of the Prior Art

[0005] Apparatuses like a projector or a projection system are types ofdisplays that realize a predetermined image on a screen by projecting alight generated at a light source onto the screen through an opticalsystem. Such displays are used in many places, namely, in meetings forpresentations, in theaters and in homes.

[0006] An optical device such as a projector realizes an image by usinga liquid crystal display (LCD) or a cathode ray tube (CRT). In order toaccomplish a large-sized screen, conventionally, the optical devicemagnifies the image on the LCD and CRT, and projects the magnified imageon the screen. This method merely magnifies the image, but cannotprovide a clear image. In order to solve this problem, an imageprojecting device using a digital micromirror device (DMD) has beensuggested and is presently in use.

[0007] The DMD has a number of micromirrors corresponding to theresolution. The micromirrors control the reflection of light inaccordance with the input signals. Briefly put, the DMD is asemiconductor optical switch using a micro-mirror. As the DMD isdigital, it has excellent color representation and brightness.

[0008]FIG. 1 is a view showing a basic structure of a conventionalprojection type image apparatus using a color wheel.

[0009] Referring to FIG. 1, the conventional projection type imageapparatus 100 using the color wheel includes a light source 110, a colorwheel 120, a light tube 130, a lens 140, a DMD panel 150 and aprojection lens 160. The one-dotted line in FIG. 1 represents an opticpath of white light.

[0010] The light source 110 can be an arc lamp or a laser, which emits awhite light. The color wheel 120 is rotated in the arrowed direction bya rotating means (not shown), and divided into a red (R), green (G) andblue (B) divisions. The white light emitted from the light source 110 ispassed through the R, G and B divisions into split rays of light, i.e.,R, G and B beams.

[0011] The light tube 130 is formed as a hollow hexahedron having athrough hole therein. The R, G and B beams from the color wheel 120 aretransformed into a square beam inside of the light tube 130. The squarebeam of the laser beam is dispersed at the lens 140 to be incident onthe DMD panel 150.

[0012] The DMD panel 150 includes a plurality of micromirrors 150 a. TheR, G and B beams of respective wavelength are reflected from themicromirrors 150 a of the DMD panel 150. The reflected R, G and B beamspass through the projection lens 160 and form an image on the screen.

[0013] Such a projection type image apparatus 100 can quickly processthe response signal to the split R, G and B beams by theindependently-driven micromirrors 150 a. In other words, color image ofgood quality can be obtained with a simpler structure. However,realizing an image using a color filter and single-plate type DMD panelusually utilizes only a third of the entire light quantity.

[0014] This is because 60-70% of the white light emitted from the lightsource is blocked at the color wheel 120. While the R beam is evenlyprojected on the entire panel, other beams, i.e., G and B are completelyblocked by the color filter and discarded. The same situation applieswith respect to the G and B beams, respectively.

[0015] Accordingly, only a third of the incident white light is utilizedaccording to the color filter method, and the brightness of the image isdeteriorated to a third. In other words, as the white light is emittedfrom the light source, passed through the color wheel and then projectedonto the panel, the entire light quantity decreases. Accordingly, thelight utilization decreases, and brightness of the realized image isalso deteriorated.

SUMMARY OF THE INVENTION

[0016] Accordingly, it is an aspect of the present invention to providean image projecting apparatus and method capable of preventing areduction of light utilization on the single panel to a third degree,and increasing a light quantity utilization using a pair of dichroicmirror wheels.

[0017] In order to accomplish the above aspect, an image projectingapparatus consistent with the present invention includes a light sourcewhich emits a plurality of monochromatic rays of light with differentwavelengths, a condenser lens which concentrates the plurality ofmonochromatic rays, a first color separating unit which rotates andselectively causes the plurality of monochromatic rays to be reflectedtherefrom or passed therethrough, a second color separating unit whichselectively causes the plurality of monochromatic rays passed throughthe first color separating unit to be reflected therefrom or passedtherethrough, a plurality of square beam generating units which areinputted with the plurality of monochromatic rays reflected from thefirst and the second color separating units and which transform themonochromatic rays as inputted into square beams, a plurality of panelunits which are inputted with the square beams of the monochromatic raysand which form a plurality of monochromatic images corresponding to themonochromatic rays, and a plurality of projecting lens units which aredisposed to face the plurality of panel units.

[0018] The first and the second color separating units each comprises adichroic mirror wheel. Each of the plurality of panel units is inputtedwith the plurality of monochromatic rays, which are reflected from thefirst and the second color separating units by predetermined order, atleast once, thereby forming an image thereon.

[0019] Each of the first and the second color separating units isdivided into a plurality of divisions where the plurality ofmonochromatic rays are selectively reflected from or passed through. Thenumber of the plurality of divisions is a multiple of three (3).

[0020] The first and the second color separating units are rotated at asame speed so that the plurality of monochromatic rays of differentwavelengths can be reflected and passed on the same optical axis. Eachof the first and the second color separating units corresponds to abasal part of a solid cone by cutting off a top by a plane parallel tothe base. The plurality of panel units each comprises a digitalmicromirror device (DMD) for modulating the plurality of monochromaticimages into a digital signal, and reflecting the signal to the pluralityof projecting lens units at a predetermined angle.

[0021] According to the present invention, by employing two dichroicmirror wheels, the R, G and B monochromatic lights are selectivelyreflected from, or passed through the two dichroic mirror wheelsaccording to wavelengths. As a result, independent images, or identicalimages can be realized on a plurality of screens even in a single paneloptical device system.

[0022] An image projecting method according to another embodiment of thepresent invention includes emitting a plurality of monochromatic rays oflight with different wavelengths through a light source, concentratingthe plurality of monochromatic rays through a condenser lens, rotatingand selectively causing the plurality of monochromatic rays to bereflected from or passed through a first color separating unit,selectively causing the plurality of monochromatic rays passed throughthe first color separating unit to be reflected from or passed through asecond color separating unit, inputting a plurality of square beamgenerating units with the plurality of monochromatic rays reflected fromthe first and the second color separating units and transforming themonochromatic rays as inputted into square beams, inputting a pluralityof panel units with the square beams of the monochromatic rays andforming a plurality of monochromatic images corresponding to themonochromatic rays, and disposing a plurality of projecting lens unitsto face the plurality of panel units.

[0023] An image projecting apparatus according to another embodiment ofthe present invention includes means for emitting a plurality ofmonochromatic rays of light with different wavelengths, means forconcentrating the plurality of monochromatic rays, means for rotatingand selectively causing the plurality of monochromatic rays to bereflected therefrom or passed therethrough, means for selectivelycausing the plurality of monochromatic rays passed through the firstcolor separating unit to be reflected therefrom or passed therethrough,means for being inputted with the plurality of monochromatic raysreflected from the first and the second color separating units andtransforming the monochromatic rays as inputted into square beams, meansfor being inputted with the square beams of the monochromatic rays andforming a plurality of monochromatic images corresponding to themonochromatic rays, and means for projecting being disposed to face theplurality of panel units.

[0024] An image projecting apparatus according to another embodiment ofthe present invention includes a light source which emits a plurality ofmonochromatic rays of light with different wavelengths, a condenser lenswhich concentrates the plurality of monochromatic rays, a first dichroicmirror wheel which rotates and selectively causes the plurality ofmonochromatic rays to be reflected therefrom or passed therethrough, asecond dichroic mirror wheel which selectively causes the plurality ofmonochromatic rays passed through the first color separating unit to bereflected therefrom or passed therethrough, a plurality of square beamgenerating units which are inputted with the plurality of monochromaticrays reflected from the first and the second dichroic mirror wheels andwhich transform the monochromatic rays as inputted into square beams, aplurality of digital micromirror devices DMD's which are inputted withthe square beams of the monochromatic rays and form a plurality ofmonochromatic images corresponding to the monochromatic rays and aplurality of projecting lens units disposed to face the plurality ofDMD's.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The above objects and other features of the present inventionwill become more apparent by describing in detail an exemplaryembodiment thereof with reference to the attached drawings, in which:

[0026]FIG. 1 is a view showing a basic structure of a conventionalprojection type image apparatus using a color wheel;

[0027]FIG. 2 is a view showing a basic structure of an image projectingapparatus according to an exemplary embodiment of the present invention;

[0028]FIG. 3 is a view showing a basic structure of a first dichroicmirror wheel and a second dichroic mirror wheel of FIG. 2;

[0029]FIGS. 4A and 4B are transverse sectional views of the first andthe second dichroic mirror wheels of FIG. 2;

[0030]FIG. 5 is another transverse sectional view of a dichroic mirrorwheel of FIG. 2; and

[0031]FIG. 6 is a longitudinal sectional view of the first and thesecond dichroic mirror wheels of FIG. 3.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

[0032] Hereinafter, the present invention will be described in detailwith reference to the accompanying drawings.

[0033]FIG. 2 is a view showing the basic structure of an imageprojecting apparatus according to an illustrative, non-limitingembodiment of the present invention.

[0034] Referring to FIG. 2, the image projecting apparatus 200 accordingto the present invention includes a light source 210, a condenser lens220, a first dichroic mirror wheel 230 as a first color separating unit,a second dichroic mirror wheel 240 as a second color separating unit,first, second and third square beam generating units 250 a, 250 b, 250c, first, second and third panel units 260 a, 260 b, 260 c, and first,second and third projection lenses 270 a, 270 b, 270 c.

[0035] In FIG. 2, a path of travel of the light passing through thefirst and the second dichroic mirror wheels 230, 240 is represented by aone-dotted line, while a path of travel of the light reflected from thefirst and the second dichroic mirror wheels 230, 240 is represented by atwo-dotted line.

[0036] The light source 210 emits white light. The white light consistsof a plurality of monochromatic lights of different wavelengths. Theplurality of monochromatic lights include red (R), green (G), and blue(B) laser beams. The light source 210 may be formed as a laser, an arclamp, a metal halide lamp, a halogen lamp or a xenon lamp.

[0037] The condenser lens 220 concentrates the R, G and B laser beamsthat are emitted from the light source 210. Preferably, the condenserlens 220 includes a pair of collimating lenses. The laser beams emittedfrom the condenser lens 220 is concentrated on the first dichroic mirrorwheel 230.

[0038] As generally known, the dichroic mirror splits the white lightfrom the light source into R, G and B laser beams in accordance with therespective wavelengths. Such a dichroic mirror is glass surface coatedwith a dielectric multi-layer, and selectively causes the light to bereflected therefrom or passed therethrough using light interference. Inother words, the laser beam is either reflected from, or passed throughthe dichroic mirror in accordance with the property of coating.

[0039]FIG. 3 is a view showing the basic structure of the first and thesecond dichroic mirror wheels 230, 240 of FIG. 2, and FIGS. 4A and 4Bare transverse sectional views showing the first and the second dichroicmirror wheels 230, 240 of FIG. 2. FIG. 5 is another transverse sectionalview of the dichroic mirror wheel 240 of FIG. 2, and FIG. 6 is alongitudinal sectional view of the first and the second dichroic mirrorwheels 230, 240 of FIG. 3.

[0040] Referring to FIG. 3, each of the first and the second dichroicmirror wheels 230, 240 is formed as a frustum-cone, i.e., the basal partof a solid cone by cutting off the top by a plane parallel to the base.The first and the second dichroic mirror wheels 230, 240 are rotated inthe arrowed direction or in a direction opposite to the arroweddirection.

[0041] The first and the second dichroic mirror wheels 230, 240 may berotated in the same direction, or oppositely, and with the samerotational speed. The first and the second dichroic mirror wheels 230,240 are rotated at the same speed so as to cause the R, G and B lightsto be reflected therefrom or passed therethrough on the same light axis.

[0042] The first and the second dichroic mirror wheels 230, 240 may bedriven by the motors (not shown) respectively provided therefor, or by asingle motor (not shown) commonly provided therefor.

[0043] Referring to FIGS. 4A and 4B, each of the first and the seconddichroic mirror wheels 230, 240 is divided into three divisions forcausing the R, G and B beams to be reflected therefrom or passedtherethrough. The divisions are coated respectively according to theproperty of the R, G and B beams, to selectively cause the R, G and Blaser beams to be reflected therefrom or passed therethrough.

[0044] More specifically, by coating the respective divisions withdifferent thickness, the first and the second dichroic mirror wheels230, 240 can selectively cause the R, G and B laser beams to bereflected therefrom or passed therethrough. For example, FIG. 4A showsthe I-division being coated to exclusively reflect the R laser beam,II-division being coated to exclusively reflect the G laser beam, andIII-division being coated to exclusively reflect the B laser beam.

[0045] The number of divisions of the dichroic mirror wheel correspondsto the multiples of 3, such as 6, 9 and so on. The dichroic mirror wheelhaving a greater number of divisions is rotated at a slower speed.

[0046] For example, the dichroic mirror wheel divided into 6 divisionsas shown in FIG. 5 is rotated at a half speed of the first and thesecond dichroic mirror wheels 230, 240 respectively having 3 divisionsdivided therein. In rotation, the dichroic mirror wheel having 6divisions realizes 60 frames of images per second.

[0047] Referring to FIG. 6, assuming that the radius of the base of eachof the first and the second dichroic mirror wheels 230, 240 is r, andthe maximum height from the base to the top is x, the radius r and themaximum height x is at an angle θ. In accordance with the angle θ, thedirection of reflection and penetration of the laser beam with respectto the respective divisions of the first and the second dichroic mirrorwheels 230, 240 is determined.

[0048] In rotation, the first dichroic mirror wheel 230 selectivelycauses the R, G and B laser beams, concentrated by the condenser lens220, to be reflected therefrom or passed therethrough. In other words,while the first dichroic mirror wheel 230 is rotated, each division ofthe first dichroic mirror wheel 230 reflects the arriving laser beamthat corresponds to the property of the material coated thereon, whilepermitting the rest of the laser beams to pass therethrough.

[0049] The second dichroic mirror wheel 240 reflects one of the laserbeams passed through the first dichroic mirror wheel 230, whilepermitting the other laser beam to pass therethrough. In other words,while the second dichroic mirror wheel 240 is rotated, each division ofthe second dichroic mirror wheel 240 reflects the arriving laser beamthat corresponds to the property of the material coated thereon, whilepermitting the other laser beam to pass therethrough.

[0050] The reflected laser beam from the first dichroic mirror wheel 230is incident on the first square beam generating unit 250 a, while thereflected laser beam from the second dichroic mirror wheel 240 isincident on the second square beam generating unit 250 b. The laser beampassed through the second dichroic mirror wheel 240 is incident on thethird square beam generating unit 250 c.

[0051] The first, the second and the third square beam generating units250 a, 250 b, 250 c transform the laser beams incident thereon intosquare beams. The first, the second and the third square beam generatingunits 250 a, 250 b, 250 c include first, second and third light tubes252 a, 252 b, 252 c and first, second and third relay lenses 254 a, 254b, 254 c, respectively.

[0052] The R, G and B beams incident on the hollow interior of thefirst, the second and the third light tubes 252 a, 252 b, 252 c from thefirst and the second dichroic mirror wheels 230, 240 are transformed tothe square beam. Each of the first, the second and the third light tubes252 a, 252 b, 252 c are formed as a hollow hexahedron having a throughhole therein. The interior of each of the first, the second and thethird light tubes 252 a, 252 b, 252 c is defined by four mirrors.

[0053] The first, the second and the third relay lenses 254 a, 254 b,254 c disperse the square beam of the R, G and B laser beams to beincident on the first, the second and the third panel units 260 a, 260b, 260 c corresponding to the respective relay lenses 254 a, 254 b, 254c. The first, the second and the third panel units 260 a, 260 b, 260 cform monochromatic images thereon with the R, G and B laser beamstransformed into the square beam and incident thereon.

[0054] A color image is formed by the combination of the R, G and Blaser beams, as the R, G and B laser beams are incident on the first,the second and the third panel units 260 a, 260 b, 260 c bypredetermined order at least once. Since the image signals of the laserbeams incident on the first, the second and the third panel units 260 a,260 b, 260 c are different, images realized on the screen 1, screen 2and screen 3 also vary.

[0055] The first, the second and the third panel units 260 a, 260 b, 260c respectively include a digital micromirror device (DMD) panel, or aliquid crystal display (LCD) panel. While the DMD panel is a reflectivepanel, the LCD panel is a transit panel. For using the LCD panel, theposition of the projection lens and the screens can be varied. Now, theoperation of the present invention will be described with reference toone example using the DMD panel.

[0056] The movable mirrors respectively provided at the first, thesecond and the third panel units 260 a, 260 b, 260 c modulate the R, Gand B monochromatic images on the first, the second and the third panelunits 260 a, 260 b, 260 c, subject the monochromatic images to thetime-division process and then reflect at a predetermined angle.

[0057] The entire image reflected from the movable mirrors of the first,the second and the third panel units 260 a, 260 b, 260 c is projectedonto a plurality of screens screen1, screen2, screen3, forming an imagethereon. The first, the second and the third projection lenses 270 a,270 b, 270 c are disposed opposite to the respective DMD panels 260 a,260 b, 260 c.

[0058] The plurality of screens screen1, screen2, screen3 may have thesame, or different size. Further, when different image signals areinputted on the DMD panels 260 a, 260 b, 260 c, images are differentlyformed on the respective screens screen1, screen2, screen3 . Sinceimages formed on the respective screens screen1, screen2, screen3 varyin accordance with the respective image signals inputted to the DMDpanels 260 a, 260 b, 260 c, different images can be formed on therespective screens screen1, screen2, screen3.

[0059] Hereinbelow, forming different color images on a plurality ofpanels 260 a, 260 b, 260 c according to an exemplaryembodiment will bedescribed with reference to table 1. TABLE 1 I-division II-divisionIII-division First Dichroic mirror wheel R: reflect G: reflect B:reflect G,B: pass R,B: pass R, G: pass ↓ ↓ ↓ IV-division V-divisionVI-division Second Dichroic mirror wheel G: reflect B: reflect R:reflect B: pass R: pass G: pass

[0060] Referring to FIGS. 4A and 4B, and table 1, the divisions Ithrough VI of the first and the second dichroic mirror wheels 230, 240are coated to a different thickness so as to selectively cause the laserbeam to be reflected therefrom or passed therethrough. Morespecifically, I and VI divisions are coated to cause the R laser beam tobe reflected therefrom, II and IV divisions are coated to cause the Glaser beam to be reflected therefrom, and III and V divisions are coatedto cause the B laser beam to be reflected therefrom.

[0061] The first and the second dichroic mirror wheels 230, 240 may berotated in the same direction or opposite directions. It should beassured that I and IV divisions, II and V divisions, and III and VIdivisions are faced with each other at least once in every rotation, andfor this purpose, the first and the second dichroic mirror wheels 230,240 are rotated at the same speed.

[0062] By doing as above, a laser beam passed through the first dichroicmirror wheel 230 can be reflected from the second dichroic mirror wheel240 while the other laser beam passed through the first dichroic mirrorwheel 230 is passed through the second dichroic mirror wheel 240. Inother words, if a certain area a of one division which reflects acertain laser beam is made to face another area α′ of the seconddichroic mirror wheel 240 that also reflects the certain laser beam, allthe laser beams are passed through another area α′ of the seconddichroic mirror wheel 240 without a reflection of light.

[0063] The above situation is prevented by rotating the first and thesecond dichroic mirror wheels 230, 240 because the R, G and Bmonochromatic lights of different wavelengths are reflected and passedon the same optical axis.

[0064] For example, it is the IV division of the second dichroic mirrorwheel 240 that can selectively cause the G and B laser beams from the Idivision of the first dichroic mirror wheel 230 to be reflected orpassed. Accordingly, the I and IV divisions need to face each other atleast once.

[0065] The method of forming one color image on the panels will bedescribed with reference to table 1.

[0066] (a) As the white light inclusive of R, G and B laser beams isemitted from the light source 210 and reaches the I division of thefirst dichroic mirror wheel 230 in rotation, R laser beam is reflectedfrom the I division, while the G and B laser beams are passed throughthe I division. The G and B laser beams are passed through the Idivision, and reach the IV division of the second dichroic mirror wheel240 in rotation. In the IV division, G laser beam is reflected and the Blaser beam is passed.

[0067] (b) As the white light reaches the II division of the firstdichroic mirror wheel 230 in rotation, G laser beam is reflected whilethe R and B laser beams are passed. The R and B laser beams are passedthrough the II division, and reach the V division of the second dichroicmirror wheel 240 in rotation. In V division, B laser beam is reflectedand R laser beam is passed.

[0068] (c) As the white light reaches the III division of the firstdichroic mirror wheel 230 in rotation, B laser beam is reflected whilethe R and G laser beams are passed. The R and G laser beams are passedthrough the III division, and reach the VI division of the seconddichroic mirror wheel 240 in rotation. In VI division, R laser beam isreflected and G laser beam is passed.

[0069] Referring to the process (a), R laser beam, which is reflectedfrom the I division, is incident on the first square beam generatingunit 250 a, forming a monochromatic image thereon. G laser beam, whichis reflected from the IV division, is incident on the second square beamgenerating unit 250 b, and B laser beam, which is passed through the IVdivision, is incident on the third square beam generating unit 250 c,respectively forming corresponding monochromatic images.

[0070] Referring to the process (b), G laser beam, which is reflectedfrom the II division, is incident on the first square generating unit250 a. B laser beam, which is reflected from the V division, is incidenton the second square beam generating unit 250 b, and R laser beam, whichis passed through the V division, is incident on the third square beamgenerating unit 250, respectively forming corresponding monochromaticimages.

[0071] Referring to the process (c), B laser beam, which is reflectedfrom the III division, is incident on the first square generating unit250 a, R laser beam, which is reflected from the VI division, isincident on the second square beam generating unit 250 b, and G laserbeam, which is passed through the VI division, is incident on the thirdsquare beam generating unit 250 c, respectively forming correspondingmonochromatic images.

[0072] By the processes (a), (b), (c), a plurality of laser beams aresuccessively incident on the first square beam generating unit 250 a andthe first panel unit 260 by order of R laser beam→G laser beam→B laserbeam, and by order of G laser beam→B laser beam→R laser beam on thesecond square beam generating unit 250 b and the second panel unit 260,and by order of B laser beam→R laser beam→G laser beam on the thirdsquare beam generating unit 250 c and the third panel unit 260 c.

[0073] After being transformed into square beams at the first, thesecond and the third square beam generating units 250 a, 250 b, 250 c,the square laser beams are projected onto the first, the second and thethird panel units 260 a, 260 b, 260 c by order described above. As aresult, one color image is realized on the respective panel units 260 a,260 b, 260 c.

[0074] For example, one color image is realized as I) R monochromaticimage with respect to R laser beam, ii) G monochromatic image withrespect to G laser beam, and iii) B monochromatic image with respect toB laser beam, are consecutively formed on the first panel unit 260 a.The monochromatic images are formed on the other panel units 260 b, 260c by order of incident of the laser beams on the second and the thirdsquare beam generating units 250 b, 250 c. As the laser beams from threedifferent monochromatic images, one color image is formed.

[0075] Considering another exemplary embodiment of the presentinvention, the respective divisions of the first and the second dichroicmirror wheels 230, 240 may be coated with the following properties inthe table 2. TABLE 2 I-division II-division III-division First Dichroicmirror wheel R: reflect G: reflect B: reflect G,B: pass R,B: pass R, G:pass ↓ ↓ ↓ IV-division V-division VI-division Second Dichroic mirrorwheel B: reflect R: reflect G: reflect G: pass B: pass R: pass

[0076] Referring to table 2, R laser beam is reflected from theI-division, while G and B laser beams are passed therethrough. Then Blaser beam is reflected from the IV-division, and the G laser beam ispassed therethrough. Further, G laser beam is reflected from theII-division, while R and B laser beams are passed therethrough. Then Rlaser beam is reflected from the V-division, and B laser beam is passedtherethrough. Further, B laser beam reflected from the III-division,while G and R laser beams are passed therethrough. Then G laser beam isreflected from the VI-division, and R laser beam is passed therethrough.

[0077] Alternatively, a complex type image projecting system thatemploys a projector instead of one screen can be used. In this case, anoperator can use the projector for presentations or the like, whilehaving different images formed on two screens. Accordingly, the imageprojecting device can be used more efficiently.

[0078] As described above, the apparatus and method for image projectingdevice according to the present invention includes two rotatabledichroic mirror wheels that selectively cause a plurality ofmonochromatic lights in white light to be reflected therefrom or passedtherethrough according to the wavelength properties. As a result,compared to the conventional system that uses a single panel and thushas a deterioration of light utilization by a third, the presentinvention has a reduced amount of discarded, or absorbed monochromaticlight, and increased light utilization. Further, independent oridentical images can be formed on a plurality of screens by using thelaser beams being reflected from, or passed through the respectivedichroic mirrors.

[0079] Although a few exemplary embodiments of the present inventionhave been described, it will be understood by those skilled in the artthat the present invention should not be limited to the describedexemplary embodiments, but various changes and modifications can be madewithin the spirit and scope of the present invention as defined by theappended claims.

What is claimed is:
 1. An image projecting apparatus, comprising: alight source which emits a plurality of monochromatic rays of light withdifferent wavelengths; a condenser lens which concentrates the pluralityof monochromatic rays; a first color separating unit which rotates andselectively causes the plurality of monochromatic rays to be reflectedtherefrom or passed therethrough; a second color separating unit whichselectively causes the plurality of monochromatic rays passed throughthe first color separating unit to be reflected therefrom or passedtherethrough; a plurality of square beam generating units which areinputted with the plurality of monochromatic rays reflected from thefirst and the second color separating units and which transform themonochromatic rays as inputted into square beams; a plurality of panelunits which are inputted with the square beams of the monochromatic raysand which form a plurality of monochromatic images corresponding to themonochromatic rays; and a plurality of projecting lens units which aredisposed to face the plurality of panel units.
 2. The image projectingapparatus of claim 1, wherein each of the first and the second colorseparating units comprises a dichroic mirror wheel.
 3. The imageprojecting apparatus of claim 1, wherein each of the plurality of panelunits is inputted with the plurality of monochromatic rays, which arereflected from the first and the second color separating units bypredetermined order, at least once, thereby forming an image thereon. 4.The image projecting apparatus of claim 1, wherein each of the first andthe second color separating units is divided into a plurality ofdivisions where the plurality of monochromatic rays are selectivelyreflected from or passed through.
 5. The image projecting apparatus ofclaim 4, wherein the number of the plurality of divisions is a multipleof three (3).
 6. The image projecting apparatus of claim 4, wherein thefirst and the second color separating units are rotated at a same speedso that the plurality of monochromatic rays of different wavelengths canbe reflected and passed on the same optical axis.
 7. The imageprojecting apparatus of claim 1, wherein each of the first and thesecond color separating units corresponds to a basal part of a solidcone by cutting off a top by a plane parallel to the base.
 8. The imageprojecting apparatus of claim 1, wherein each of the plurality of panelunits comprises a digital micromirror device (DMD) for modulating theplurality of monochromatic images into a digital signal, and reflectingthe signal to the plurality of projecting lens units at a predeterminedangle.
 9. An image projecting method, comprising: emitting a pluralityof monochromatic rays of light with different wavelengths through alight source; concentrating the plurality of monochromatic rays througha condenser lens; rotating and selectively causing the plurality ofmonochromatic rays to be reflected from or passed through a first colorseparating unit; selectively causing the plurality of monochromatic rayspassed through the first color separating unit to be reflected from orpassed through a second color separating unit; inputting a plurality ofsquare beam generating units with the plurality of monochromatic raysreflected from the first and the second color separating units andtransforming the monochromatic rays as inputted into square beams;inputting a plurality of panel units with the square beams of themonochromatic rays and forming a plurality of monochromatic imagescorresponding to the monochromatic rays; and disposing a plurality ofprojecting lens units to face the plurality of panel units.
 10. An imageprojecting apparatus, comprising: means for emitting a plurality ofmonochromatic rays of light with different wavelengths; means forconcentrating the plurality of monochromatic rays; means for rotatingand selectively causing the plurality of monochromatic rays to bereflected therefrom or passed therethrough; means for selectivelycausing the plurality of monochromatic rays passed through the firstcolor separating unit to be reflected therefrom or passed therethrough;means for being inputted with the plurality of monochromatic raysreflected from the first and the second color separating units andtransforming the monochromatic rays as inputted into square beams; meansfor being inputted with the square beams of the monochromatic rays andforming a plurality of monochromatic images corresponding to themonochromatic rays; and means for projecting being disposed to face theplurality of panel units.